implement gain dialog with AGC option

htdocs/lib/settings/GainInput.js

@@ -0,0 +1,22 @@
+$.fn.gainInput = function() {
+    this.each(function() {
+        var $container = $(this);
+
+        var update = function(value){
+            $container.find('.option').hide();
+            $container.find('.option.' + value).show();
+        }
+
+        var $select = $container.find('select');
+        $select.on('change', function(e) {
+            var value = $(e.target).val()
+            update(value);
+            if (value == 'auto') {
+                $input.val('auto');
+            } else {
+                $input
+            }
+        });
+        update($select.val());
+    });
+}

htdocs/settings.js

@@ -1,8 +1,8 @@
 $(function(){
     $('.map-input').mapInput();
-    $('.sdrdevice').sdrdevice();
     $('.imageupload').imageUpload();
     $('.bookmarks').bookmarktable();
     $('.wsjt-decoding-depths').wsjtDecodingDepthsInput();
     $('#waterfall_scheme').waterfallDropdown();
+    $('#rf_gain').gainInput();
 });